The most common of all feline hematopoietic cancers, lymphosarcoma (LSA) is known to be caused by an oncornavirus, the feline leukemia virus (FeLV). This virus is also known to cause three other diseases; nonregenerative anemia, a panleukopenia-like syndrome and thymic anemia. It is also associated with, but not yet proved to be the cause of other abnormalities such as myeloproliferative disorders and fetal abortions. It is known the FeLV can grow on the cells of other mammalian species including man and dogs, although it is not clear that the virus is capable of infecting these mammals. Clearly a procedure for protecting against infection by FeLV would be of great value.
It has been observed that some cats can develop immunity to FeLV infections. The development of an effective vaccine, therefore, has appeared to be possible. There are four possible types of FeLV vaccines. These are (a) those consisting primarily of live attenuated FeLV, (b) those consisting of killed FeLV, (c) those produced from cells infected with FeLV, and (d) those composed of FeLV subunits.
U.S. Pat. No. 4,034,081 is based on a divisional application of the application which resulted in the issuance of U.S. Pat. No. 3,966,907. Both patents describe vaccines based on virus which are killed, for example, by irradiation, hydroxylamine, or paraformaldehyde; or inactivated, for example by mitomycin D. The patents also describe vaccines based on cells infected with FeLV.
Oncornaviruses such as murine leukemia virus (MuLV) Rausher and Friend strains, R-MuLV and F-uLV as well as FeLV are known to contain two outer envelope subunits. These are: (1) a glycoprotein with an approximate molecular weight of 70,000 daltons, and (2) a nonglycosylated protein with an approximate molecular weight of 15,000 daltons. These are commonly designated gp70 and p15 (E). The former subunit has also been referred to as gp71; see Fischinger et al, Virology 71, 169 (1976) and Noranha et al, Virology 85, 617 (1978).
The individual subunits gp70 and p15 (E) have been utilized to produce antisera to FeLV and MuLV in goats and this antisera has been utilized to produce passive immunity to FeLV in cats, see Fischinger et al and Noronha et al infra. No vaccines for FeLV capable of producing long term effects based on viral subunits have yet been described.